The inventive concept relates generally to semiconductor memory devices. More particularly, embodiments of the inventive concept relate to nonvolatile memory devices incorporating memory cells programmed in accordance with a constituent magnetization layer. Other embodiments of the inventive concept relate to write methods capable of programming such nonvolatile memory devices.
The demand for nonvolatile, random access memory (RAM) devices having dense memory cell integration and acceptable data access speeds has increased over the past years. Flash memory devices have historically met much of the demand for nonvolatile memory in handheld electronic devices. However, research and development directed to other types of nonvolatile memory have continued in the ongoing quest for improved memory system performance. For example, contemporary research and development has been directed to the ferroelectric RAM (FRAM) that uses a ferroelectric capacitor, the magnetic RAM (MRAM) that uses a tunneling magneto-resistive (TRM) film, the phase-change RAM (PRAM) that uses one or more chalcogenide alloys, and the resistive RAM (RRAM) that uses a variable resistance material. Each of these “alternate nonvolatile memory types” has been proposed as a possible replacement for flash memory.
Of important note, a memory cell in each of these alternate nonvolatile memory types is capable of being directly “overwritten” with data without the need to first erase previously stored data as is the case with flash memory. However, such alternate nonvolatile memory devices require different respective “biases” according to the logical values to be written in constituent memory cells. For example, the current or voltage level required to write a logical ‘1’ value in a memory cell may be different than the current or voltage level required to write a logical ‘0’ value. Additionally, the write speed(s) and/or data integrity associated with different logical values vary according to alternate nonvolatile memory type.
Generally speaking and regardless of nonvolatile memory type being considered, any performance and/or operational difference related to respective data values to be written to a nonvolatile memory cell may be termed a “write-asymmetry” characteristic. Such characteristics must be carefully considered in the design and operation of any alternate nonvolatile memory system.